A high-temperature superconducting filament and cable, and a method for manufacturing same. The substrate used to grow the superconducting layer is removed, and the exfoliated superconducting layer is coated with a protective layer, and then sliced into narrow strips. The strips are thereafter encapsulated with a conductive metal to provide a high-temperature superconducting filament. The filaments may be bundled together to provide a high-temperature superconducting cable.
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1. A method for manufacturing a multi-ply high-temperature superconducting wire from a second generation wire, said second generation wire including a superconducting layer positioned upon a metal substrate, said second generation wire further including a buffer layer positioned between said superconducting layer and said metal substrate, the method comprising the steps of:
a) separating said superconducting layer from said metal substrate to provide an exfoliated superconducting tape, said exfoliated superconducting tape including a superconducting layer in the absence of a buffer layer and a metal substrate;
b) stacking lengths of said exfoliated superconducting tape; and
c) laser slicing said stacked exfoliated superconducting tape into narrow strips to provide said multi-ply high-temperature superconducting wire, said multi-ply high-temperature superconducting wire having multiple superconducting layers.
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This invention was made with government support under Contract No. DE-SC0013856 awarded by the Department of Energy. The government has certain rights in the invention.
The present invention relates to high-temperature superconducting yttrium-barium-copper-oxide filaments and cable, and to a process for manufacturing same via the exfoliation of a superconducting layer from an epitaxial substrate.
The advent of second generation (2G) YBa2Cu3O7 (YBCO) wire technology has spawned impressive technological progress since the first meter of 2G wire was manufactured in 1995. Further developments in the field have been driven by existing and emerging applications, such as fault current limiters, transformers, and wind turbines. The second generation superconducting (2G) wires have record high upper critical field and critical temperature, potentially enabling design of high-temperature superconducting magnets, which could be cooled with inexpensive single-stage cryocoolers. The core 2G wire technology can be described as a thin (<2 micron) YBCO layer deposited on a 50-100 micron thick metal substrate.
Commercially-available 2G wires, such as the wire shown in
The current design of 2G wire magnets can be described as a flat “pancake” stack.
There is therefore a need in the art for high-temperature superconducting filaments which can be used, for example, to manufacture superconducting magnets with reduced/eliminated risk of delamination of the superconducting layer, without the need to utilize discreet pancakes and diagonal splicing, and with enhanced mechanical properties. There is a further need in the art for a high-temperature superconducting cable which can be used for power transmission with reduced magnetization losses. There is a still further need in the art for a fault current limiter utilizing superconducting materials which exhibits reduced magnetization losses. Finally, there is a need in the art for a method of manufacturing high-temperature superconducting filaments and cables with reduced/eliminated risk of delamination of the superconducting layer, which exhibit more uniform electrical properties, which exhibit enhanced mechanical properties, and which may be readily spliced together.
The present invention, which addresses the needs of the art, relates to a method for manufacturing high-temperature superconducting filaments from a 2G wire. The 2G wire includes a superconducting layer positioned upon a metal substrate. The method includes the step of separating the superconducting layer from the metal substrate, thereby providing an exfoliated superconducting tape. The exfoliated superconducting tape is thereafter sliced into narrow strips. The narrow strips are then encapsulated to provide the high-temperature superconducting filaments. In one preferred embodiment, the exfoliated superconducting tape is coated with a protective layer prior to the slicing of the tape into the narrow strips. In another preferred embodiment, the narrow strips are encapsulated with an electrically-conductive material, e.g., via i) soldering of a metal stabilizer thereabout, or ii) galvanically electroplating a conductive metal (e.g., copper) thereabout. In still another embodiment, lengths of the exfoliated superconducting tape are stacked prior to the slicing of the tape into the narrow strips, thereby providing multi-ply strips including multiple conductors. A metal stabilizer layer may be positioned between adjacent lengths of the stacked exfoliated superconducting tape. In one preferred embodiment, the individual filaments are spliced together to provide an extended length of continuous filament. In certain embodiments, the length of the superconducting filament is greater than 100 meters and the width is between 1-2 mm. In still other embodiments, the exfoliation is accomplished by rapidly heating the substrate with an inductive coil. In still other embodiments, the exfoliation is accomplished by deformation of the tape before the exfoliation. In still other embodiments, the exfoliation is accomplished by irradiation of the tape with energetic ions.
The present invention further relates to a method for manufacturing a length of high-temperature superconducting cable from a 2G wire. The 2G wire includes a superconducting layer positioned upon a metal substrate. The method includes the step of separating the superconducting layer from the metal substrate, thereby providing an exfoliated superconducting tape. The exfoliated superconducting tape is thereafter sliced into narrow strips. The narrow strips are then encapsulated to provide the high-temperature superconducting filaments. In one preferred embodiment, the exfoliated superconducting tape is coated with a protective layer prior to the slicing of the tape into the narrow strips. In another preferred embodiment, the narrow strips are encapsulated with an electrically-conductive material, e.g., via i) soldering of a metal stabilizer thereabout, or ii) galvanically electroplating a conductive metal (e.g., copper) thereabout. In still another embodiment, lengths of the exfoliated superconducting tape are stacked prior to the slicing of the tape into the narrow strips, thereby providing multi-ply strips including multiple conductors. A metal stabilizer layer may be positioned between adjacent lengths of the stacked exfoliated superconducting tape. The high-temperature superconducting filaments are thereafter bundled into a superconducting cable. In one preferred embodiment, the individual filaments are spliced together to provide an extended length of continuous filament. In another preferred embodiment, the superconducting cable is wrapped with a conductive metal tape to protect the filaments and to provide additional quench stability. In certain embodiments, the length of the superconducting cable is greater than 100 meters and the width is between 1-2 mm. In still other embodiments, the filaments are twisted in order to reduce the magnetization loss of the cable. In still other embodiments, the number of filaments is between 1 and 100. In still other embodiments, the exfoliation is accomplished by rapidly heating the substrate with an inductive coil. In still other embodiments, the exfoliation is accomplished by deformation of the tape before the exfoliation. In still other embodiments, the exfoliation is accomplished by irradiation of the tape with energetic ions. In still other embodiments, the filaments are transposed to reduce the electrical loss of the cable.
The present invention further relates to a high-temperature superconducting filament. The filament includes a superconducting layer having a protective coating substantially covering each surface thereof. The filament further includes at least one metallic stabilizing layer adhered thereto. The filament is encapsulated within an electrically-conductive material. Finally, the filament is encapsulated in the absence of a buffer layer and in the absence of a superconductor substrate layer whereby both surfaces of the superconducting layer are in substantially equal electrical conduct with the electrically-conductive material surrounding the superconductor. In one preferred embodiment, the filament is encapsulated in the absence of a ferromagnetic material or layer. In another preferred embodiment, the electrically-conductive material is a metal stabilizer soldered about the exterior thereof. In another preferred embodiment, the electrically-conductive material is a conductive metal galvanically electroplated about the exterior thereof. In still another embodiment, the filament includes multiple stacked superconductors. In another embodiment, the filament includes multiple stacked superconductors having a metal stabilizer layer positioned between adjacent stacks. In certain embodiments, the length of the superconducting filament is greater than 100 meters and the width is between 1-2 mm.
The present invention further relates to a high-temperature superconducting cable. The cable includes a plurality of twisted filaments. Each of the filaments includes a superconducting layer having a protective coating substantially covering each surface thereof. The filament further includes at least one metallic stabilizing layer adhered thereto. The filament is encapsulated within an electrically-conductive material. Finally, the filament is encapsulated in the absence of a buffer layer and in the absence of a superconductor substrate layer whereby both surfaces of the superconducting layer are in substantially equal electrical conduct with the electrically-conductive material surrounding the superconductor. In one preferred embodiment, the filament is encapsulated in the absence of a ferromagnetic material or layer. In another preferred embodiment, the electrically-conductive material is a metal stabilizer soldered about the exterior thereof. In another preferred embodiment, the electrically-conductive material is a conductive metal galvanically electroplated about the exterior thereof. In still another embodiment, the filament includes multiple stacked superconductors. In another embodiment, the filament includes multiple stacked superconductors having a metal stabilizer layer positioned between adjacent stacks. In one preferred embodiment, the cable further includes a protective metallic tape wrapped thereabout. In certain embodiments, the length of the superconducting cable is greater than 100 meters and the width is between 1-2 mm. In still other embodiments, the filaments are twisted in order to reduce the magnetization loss of the cable. In still other embodiments, the number of filaments is between 1 and 100. In still other embodiments, the filaments are transposed to reduce the electrical loss of the cable.
Additional features, advantages, and embodiments of the present invention may be set forth from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the present disclosure and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the present disclosure claimed.
A second generation (2G) tape, i.e., tape 300, is shown in
The substrate 303 may include texture that is inherited by the buffer layer 302 and the superconducting layer 301. The texture describes a microstructure of the superconducting layer 301, including crystal plane alignment. The aligned superconducting layer 301 has a critical current density much higher than a polycrystalline (non-textured) superconductor. The textured substrate may be a flexible metal film or one of the other layers described above.
The substrate may be produced by a variety of processes. In one embodiment, the substrate is manufactured by a so-called rolling-assisted biaxially textured substrate (RABiTS) process. The RABiTS-coated conductor substrate is comprised of textured Ni or other Ni-alloy metal tape coated with an oxide buffer.
In another embodiment, the substrate may be produced by a process known as ion-beam assisted deposition (IBAD). The IBAD coated conductor is comprised of a non-textured metal film substrate, a sequence of oxide buffer layers, a superconductor layer, and a metallic stabilizer layer.
It is understood that other methods or materials can be used to construct similar tapes, and that they can also be used in accordance with this invention.
The superconducting layer, formed of YBCO or Bi-based HTS materials, may be deposited by any known process. According to one embodiment, the superconducting layer may be deposited by pulsed laser deposition. According to another embodiment, the superconducting layer may be deposited by metal-organic chemical vapor deposition (MOCVD). In another embodiment, the superconducting layer is deposited by metal-organic deposition (MOD). The superconducting layer may have any thickness, but is typically less than 10 microns.
A protective metal 501 layer may be deposited over the superconductor layer of the superconducting tape for the purposes of protecting the superconductor layer and providing a path for the electrical current if the superconductor becomes locally resistive due to overheating or spontaneous loss of superconductivity. The superconducting layer in the resistive state has the specific electrical resistivity of 300 μΩ*cm. If the electrical current is allowed to flow through the resistive part of the superconducting layer, the heat dissipation will most likely result in a catastrophic destruction of the conductor. Copper or silver have a specific electrical resistivity of approximately 2 μΩ*cm, which allows for safe diversion of the electrical current away from the resistive part of the superconductor. The protective metal layer may be any suitable metal alloy. According to one embodiment, the protective metal layer is a silver layer deposited by magnetron sputtering.
A stabilizer layer may be deposited over the protective metal layer. In one embodiment, the stabilizer layer may be a copper foil soldered to the silver coating by a low-temperature solder. The foil thickness is preferably greater than 25 microns. In another embodiment, the stabilizer is deposited by electroplating.
The superconducting layer may be formed of any appropriate superconductor. According to one embodiment, the superconductor layer may be a rare earth metal-alkaline earth metal-transition metal-oxide superconductor.
In one embodiment, the encapsulated filaments of the present invention are bundled together with strips of conductive metal, such as copper, in order to form a composite cable. An example of such a cable, i.e., cable 700, is shown in
In another embodiment, a stabilizing copper layer is deposited on the narrow strip by a galvanic process. The metal layer is deposited by passing the narrow strip through an electroplating bath filled with either basic or acidic copper solution. In a preferred embodiment, the deposited copper thickness is greater than 10 microns.
The increased critical current properties of the present filaments/cables makes such filaments/cables particularly suitable for applications involving high current density wherein reduced AC loss is desired. The filaments/cable may be used in fast-ramping superconducting magnets, generators, and transformers.
In one embodiment, the present invention provides a superconducting magnet. The magnet includes an extended length of continuous filament wound into a preselected configuration to provide a solenoid. It will be appreciated by those skilled in the art that an extended length of continuous filament eliminates the need to form discreet pancakes, and the further need to electrically splice such pancakes together. Due to narrow width of the filament, the magnet has proportionally lower magnetization loss, resulting in reduced loss of coolant, for example liquid Helium, during the magnet charge and discharge.
In another embodiment, the present invention provides an electrical transmission cable. The transmission cable includes a plurality of bundled filaments. The layers of the filaments preferably exclude all ferromagnetic materials. The superconducting layer is preferably stabilized with a high resistance metal. It will be appreciated by those skilled in the art that the elimination of any ferromagnetic layers within the filament will reduce the losses associated with magnetization of the ferromagnetic layers during transmission of power, thus providing increased efficiency and cost savings.
In a further embodiment, the present invention provides a fault current limiter for an electrical grid. The fault current limiter includes filaments wherein the superconducting layer is preferably stabilized with a high resistance metal. The filaments are preferably sliced and twisted to reduce magnetization, and the losses associated therewith. The filaments preferably do not contain any ferromagnetic material, which eliminates losses due to the magnetization of the device by the AC current during operation.
In the accompanying detailed description, reference is made to the accompanying drawings, which form a part hereof. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present invention, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure.
A standard wire (8602-FCL) offered by the AMSC Corp was used for the exfoliation experiments. The wire was a 10 mm wide YBCO-RABiTS tape soldered between two 12 mm wide layers of 75 μm thick 316L stainless steel foil. The YBCO layer was exfoliated after mechanically trimming the side fillets of the tape. In order to facilitate the YBCO layer delamination, the tape was rapidly heated by an inductive coil coupled to the tape. The inductive coil included 8 turns of gauge 14 litz wire wound to conform to a 16 cm long and 1 cm wide race-track shape. The coil was placed directly under the tape, which ensured good coupling of the tape to the AC field created by the coil. The coil was energized for 1-2 seconds by applying approximately 200 W of AC power, 50 KHz. The YBCO layer was immediately exfoliated from the substrate. Lengths of tape approximately 10 cm long were exfoliated in a typical run. These lengths of tape were then sliced into 1 mm-4 mm coupons by a CO2 laser. The laser was a Kern Mirco Laser system, which included a moving table and a 260 W CO2 laser. The cutting was assisted by the flow of nitrogen gas. The laser was operated at 20% power and was able to cut the strips at approximately 1 inch per second. Two-ply test coupons of various widths were prepared by soldering two lengths of exfoliated superconducting tape to a 25 micron thick copper foil using a In95%-Ag5% soldering alloy.
The transport critical current of wire coupons prepared in accordance with Example 1 was measured at 77K as a function of the width of the strip. For the measurements, the strips were soldered to 10 mm wide, 50 micron thick copper current leads using a low-temperature indium-based solder. The voltage leads were 25 micron thick copper wires attached to the strips by the low-temperature solder. The wire coupons were mounted on a test fixture and the fixture was immersed in a liquid nitrogen bath. DC current was gradually increased and the voltage was recorded as a function of the current (I-V curve).
The specific resistivity, defined as the resistance times the joint area, is an important parameter of a conductor. It is well known that the best results are achieved with two-component alloys, e.g., SnAg, InSn, SnPb, with RE123 pre-tinned or with an aluminum heater block to press the joint surfaces during the soldering process. In general, measured specific resistivity at 77 K ranges from >30 nΩ/cm2 to <500 nΩ/cm2. In order to determine the surface resistance of the exfoliated YBCO surface, a splice of 3 mm wide filaments was prepared by soldering the filaments face to face using Indium. The I-V curves of the filament and the splice were recorded at 77 K.
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